This invention relates to screening machines of the type used to separate or classify mixtures of solid particles of different sizes. The invention also relates to screening machines of the type used for liquid/solid separations, i.e., for separating solid particles of specific sizes from a liquid in which they are carried. More particularly, the invention relates to an improved screen panel for use within the screening machine.
In screening machines of the type described, a screen (which may be woven, an aperture plate or another design) is mounted in what is often called a “screen frame” or “screen deck” which includes a supporting peripheral frame around the perimeter of the screen. Some screens are tensioned when they are installed in the screening machine and other screens are pre-tensioned in a frame prior to being installed in the machine. Typically associated with the screen deck are other material handling elements which are moved with the screen and form walls or partitions above or below the screen for containing the liquid and/or particulate materials adjacent to the screen and directing them to appropriate outlets. These elements may comprise a top cover and a pan beneath the screen deck. In the case of screening machines with multiple screens or deck units, spacer pans or frames are provided between the multiple screens.
The screens are often removed from the screening machines for cleaning, replacement, readjustment or installation of a screen of a different mesh size or the like. The screen is releasably mounted to a carrier, table or box to which vibratory motion is imparted, typically by one or more eccentric motors or other means of excitation. The carrier, table or box is referred to herein as a “vibratory carrier”. The vibratory carrier may be moved in oscillatory, vibratory, gyratory, gyratory reciprocating, fully gyratory, rotary or another type of motion or combinations thereof, all of which are herein collectively referred to as “vibratory” motion or variations of that term.
In large commercial screening machines, the weight of the various components including the screen assembly carried by the vibratory carrier, and the weight of the material being processed on the screen assembly may total several hundred pounds or more. Screening machines which tension the screen, as opposed to those utilizing pre-tensioned screens, include the added weight associated with the screen tensioning mechanism and related components. This presents a very substantial inertial mass which resists the changes of motion applied thereto by the vibratory drive acting through the vibratory carrier. As a result of these inertial forces, a relative motion may exist between the vibratory carrier and the screen assembly. Typically, the screen assembly and vibratory carrier are each constructed of metal which could result in significant noise, wear and damage due to the relative motion or rubbing action there between. The resulting impact forces between the screen assembly and vibratory carrier significantly increase the stresses on the components and reduce their useful life.
Reducing the metal-to-metal contact minimizes the wear on the various metal components and the noise associated with the operation of the screening machine. Currently, certain screen assembly designs may not be sealed or secured relative to the remainder of the screening machine, particularly in larger screening machines. This results in the above-described metal-to-metal contact between the screen assembly and the remainder of the screening machine and prevents the screening of very fine material, such as sand or the like. The screens in larger screening machines are typically inserted and/or removed from the machine in a generally horizontal, longitudinal direction typically through an opening or slot at the head or foot end of the machine. This method of installation and removal of the screen is detrimental to known sealing arrangements because a seal which would engage the screen assembly could be torn or damaged during the installation/removal of the screen. In other screening machines, the screen is inserted vertically, typically from the top of the machine. Access to the screens from the top of the machine or the longitudinal ends is often very inconvenient and difficult.